Droppable wing tank incorporating additional wing area



Jan. 9, 1951 A. E. OSTROFF 2,537,369

DROPPABLE WING TANK INCORPORATING ADDITIONAL WING AREA Filed Jan. 29, 1948 4 g ft @My/M,

HIS ATTORNEYS.

Patented Jan. 9, 1951 DROPPABLE WING TANK INCORPORATING ADDITIONAL WING AREA Alexander E. Ostroff, St. Louis, Mo., assignor to McDonnell Aircraft Corporation, St. Louis, Mo., a corporation of Maryland Application January 29, 1948, Serial No. 5,036

8 Claims.

This invention relates to aircraft and is more particularly directed to aircraft of the type having droppable wing tips with auxiliary fuel tanks secured thereto.

A serious practicable objection to the addition of droppable fuel tanks to airplanes, particularly those whose wings have a pronounced sweep, is that the center of gravity of the airplane is shifted either too far forward or backward with relation to the mean aerodynamic chord and thus rendering the airplane unstable and uncontrollable. The principal object of the present invention is to devise an airplane of the above'type in which the droppable fuel tank is attached to supporting wing tips which are shaped and arranged to shift the mean aerodynamic chord toward or away from the fuselage a distance sufficient to re-establish th proper relationship be-' tween it and the center of gravity and thus render the airplane stable and controllable both before and after the wing tips and fuel tanks are jettisoned.

Another object of the invention is to provide an aircraft having a wing normal to or swept back or forward with respect to the longitudinal axis of the fuselage and provided with a stub wing including a fuel tank, said stub wing so related to the first mentioned wing so that the movement of the center of gravity of the plane as the fuel load is decreased is confined to predetermined limits in a lateral horizontal plane along one mean aerodynamic chord and when the tip and its tank are jettisoned, the reverse movement of the center of gravity with relation to another mean aerodynamic chord will be confined to a predetermined limit so that the aircraft stability will be maintained providing for ease of. the aircraft control and maneuverability.

Another object of this invention is to provide a droppable wing tip having a fuel tank attached thereto that may be dropped at the option of the pilot and which is so constructed and arranged with reference to the main wing of the aircraft so that the limits of movement of the center of gravity of the aircraft as the fuel tank on the drop wing tip is emptied and then dropped will vary only between narrow limits so that the stability of the aircraft will remain substantially constant.

wing tip is provided with an end surface 3, as shown in the drawings, and a stub wing 1 provided with a complemental end surface 5 that is positionable adjacent to the surface 3. A fuel tank 6 is suspended from or embodied in the wing tip 4 and suitable brackets l are secured to the internal structure of wing 2, eachbracket being provided with eyes 8, 8 which cooperate with eye 9 on each of the brackets it that are suitably securedto the fuel tank 6. A pair of I pins I, I, I! is associated with a contracting and expanding mechanism l2 provided with a screw H I 3 havingright and left hand threads thereon which engage in right and left hand nut-s incorporated in the expanding and contracting mechanism I2. The screw it? is operated by a reversible motor M' whose direction of rotation and f operation is controlled from a station in the cabin orfuselage withinconvenient reach of the pilot. When the motor. It is rotated in one direction, pins l I will secure wing tip 4 to the wing 2 and when rotated in the opposite direction,

they will be withdrawn from the eyes in the, 5 brackets so that the tank 6 and wing 4 may be,

detached from the wing 2. Fig. 1 shows the pins inserted in the eyes of the brackets and Fig. 3 shows the pins withdrawn so that the wings 4 and 6 are detached therefrom and in condition for droppingjherefrom.

The need for increased range of aircraft without increasing the over-all size of the basic airplane has required the use of external fuel tanks.

These tanks create an additional dra when inis that they are used only during the time that the plane is cruising andconsequently operate at a relatively high lift co-efficient where the in--v duced drag is an important part of the total drag I of the plane and consequently the aspect ratio plays an important part. The effective aspect,

ratio is increased by adding end plates on the wing tips and this situation is substantially similar to that created bythe placing of external wing tanks at the wing tips. Therefore, in the cruising range, the tip tanks tend to reduce the induced dragand thereby partially or totally I compensate for their friction and form drag. The use of swept back wings for high speed air H craft introduces other problems that must be considered and solved in order that the center of gravity will be confined to predetermined narrow limits of motion.

As indicated in the drawings, various circles are shown on the plan view of the wing and the portion of the fuselage structure illustrated.

As shown .-in;Fig-. 1, [5 designates thecenter of 1 gravity of the/plane whenthe wingtip tank is empty and 28 indicates the approximate 1ocation of the wing center of gravity when the tip tank is partially filled and thercircle 2| indicates the approximate location of thepenter of gravity. of the tip tank when it is filled. As "will be noted by the center of gravity. locations, in Fig.4-

of the drawings, the wing tip tankis considerablyv aft of the airplane center of gravity. Consequentl the center of gravity of theplane moves rearwardly when the tank and wing are installed. Rearward movement of the center-of gravity outside of a permissible percentage range results in an-inability to maintain the plane: stable when in operation. Permissible move ments are defined as apercentage of the mean aerodynamic chord. .The meanaerodynamic chord is a chord of a theoretical rectangular wing which would produce the same aerodynamic ef feet-as the actual wing. In Fig. 1 of .the draw- 0 ings the line -A-A represents the mean .aero-. dynamic chord of the wing without a. tiputank It should be noted thatthe: centersof .gravity.

of :the wing without the tip. tank is at of the mean aerodynamic: chord but when the tip. tank is installed, thecenter of gravity; moves aft to 35% of the -mean aerodynamic chord. Generally speaking. 25% of the mean aero-v dynamic chord is anacceptable position ofthe center of gravityv but 3.5% will ,be too .far. aft and leads to the aforesaidstability .proble However, this situationuis corrected -by .adding a stub .wing 4 to theoutboardside. 'of .the tip tank.-

This .stub..-wing..will .change ,the position of the mean aerodynamicchordto the 1ine,B+B. I

It ;will now be noted thatthei most aft center of gravity position with the tank installed is 27% of this new.,or combined mean-aerodynamic mean aerodyriamicfchord which might be too far forward for good handling and stable operation of the plane. However, at this point, the pilot jettison-s theftip tank and the stub wing whereupon the mean aerodynamic .chord -re-- turns to the line A-A. The'wing center of gravityflnowis, therefore, at 25% of the-meanaerodynamic chord line A VA, thus locating. it at a p0Siti0n' Within the safe .predetermined range of moticnof the center of gravity.

The' application .of a stub wing to a jettison able external tank in-the manner illustrated is suchthat the meaniaerodynamic chord of they main and stub .wing: combined is fplaceddnan advantageous position with respect to the plane center of gravity. An additional efiortis gained by the stub lwing which provides an increase in aspect ratio and .a decrease in induced drag. Also, the wing area is increased,therebyreducing thewing loading fortakeoffandclimbing: It should benoted that the.anglei C and the area of the stub...wing can bevaried to any ..desired value so that. .themostrdesirable, location of the mean aerodynamic chord is obtained.

The -movement of the center of .g'ravityin .a

horizontal plane with respect to themean ae 1todynamic chordin anykaircraftcan :be controlled by relatingia wingz tip-,-not.provided witha fuel;..

tank zto theqtmain. iwing so ithat lsaidpcenter v.of 1- gravity movement will be confined to certain after said. fuel tank has been emptied so that narrowly defined limits as the plane loadchanges whether .the'wings project at rightzangles' from the fuselage or are swept back therefrom or extend outwardly from the fuselage in any other direction.

What I claim is:

1. In an aircraft, a fuselage; a swept back wing secured to said fuselage, whose mean aerodynamic chord:is in one position; an auxiliary fuel tank; a droppable wing tip for supporting said ,tank and, securable to said wing and so shaped as to shift'the mean aerodynamic chord of said Wingjn parallel relation thereto outwardly from the fuselage, said wing tip and tank maintaining the center of gravity of said wing fuselage, tip and tank within an-allowable per., centage range of movement along said lastmene tioned chord; and means for releasing said. droppable wing tip and tank from said swing thee-enter of gravity .of said wing and fuselage, is maintained within allowable percentage ,rangc of movement along the. first mentionedmmean, aerodynamic chord of said wing.

2. In an aircraft, a fuselage; a sweptback wing secured thereto; anda fuel tank providedwith a forwardly projecting stub wing and.,se-. curable to said wing, said forwardly projecting stub wing so related to said wing that themovee ment of the center of gravityof .said winglas related to itsmean aerodynamic chord willlbeh confined to predetermined limits, and when .the.,,-. wing tip and tank are detached from said .wingm; the movement of the centerrof gravityrwill be confined to predetermined limits with refer,-

ence to a mean aerodynamic chord displaced. i from said first mentioned chord.

3. In an aircraft, afuselage; a swept back wing secured to said fuselage; anauxiliary ,fueltank; a droppable wing for supporting. said. tankand i; secured to the outboard end. of said Wing and r so related thereto that the percentagerange ofv movement of the center of gravity of the aircraft will be confined to predetermined limits along its" meanaerodynamic chord when the .wingitank'; is being emptied but moving beyond said range after the tank is emptied; and means. forreleas-' ing said droppable wing from said swept back wing. after said wing tank is emptied for causing i the mean aerodynamic chord of the aircraft to be shifted, the center of gravity. of the aircraft thenbeing shifted for movement. along 'the' last mentioned mean aerodynamic .chord within-jam allowable percentage range.

4. In an aircraft, a fuselage; aswept back wing. secured to said fuselage said wing and; fuselage having a mean aerodynamic chord along which the center. of gravity thereof moves within allowable percentage range undernormal loading-pa detachable swept forward tip for said wing; and" means for loading said tip, said tip and 'said means shifting the mean aerodynamic chord .of

the aircraft outwardly so that the center 'ofgravity of said fuselage, tip and said means'for longitudinal axis .is angularly disposed with.

respect to the longitudinal axis of .said wingiand means for loading said wing tip, said tip and said means shifting the mean aerodynamic chord of the aircraft outwardly so that the center of gravity of said fuselage, wing, wing tip and said means for loading being movable within an allowable percentage range along the displaced mean aerodynamic chord.

6. In an aircraft, a fuselage; a swept back wing secured to said fuselage, the center of gravity of said fuselage and wing moving within an allowable percentage range of movement along the mean aerodynamic chord of the aircraft; a detachable wing tip for stabilizing the aircraft when said aircraft is loaded so as to cause the center of gravity to move beyond the allowable range of movement along said mean aerodynamic chord, said detachable wing displacing said chord so that the center of gravity of said fuselage and wing tip moves within the allow-'- able percentage range along said displaced chord; and means for detaching said wing tip after said aircraft loading is varied so that the percentage range of movement of the center of gravity along the displaced chord is greater than that allowable for restoring the center of gravity movement to the allowable percentage range of movement along said first mentioned chord.

7. In an aircraft, a fuselage; a swept back wing secured to said fuselage, the center of gravity of said fuselage and wing moving within an allowable percentage range along the mean aerodynamic chord of said fuselage and wing; an auxiliary fuel tank; a detachable wing tip for supporting said tank and stabilizing said aircraft when said tank is filled, said tip and tank displacing the mean aerodynamic chord so that the center of gravity of said fuselage, wing, wing tip and tank moves within an allowable percentage range of movement along the displaced chord; means for detaching said wing tip after the fuel tank is emptied, the wing tip and tank causing the center of gravity to move along the displaced chord beyond the allowable percentage range of movement, the center of gravity after the detachment of the wing tip and tank being restored to movement along said first mentioned chord and Within the allowable percentage range.

8. In an aircraft, a fuselage; a swept back wing secured to said fuselage, the center of gravity of said fuselage and wing moving within an allowable percentage range along the mean aerodynamic chord of said fuselage and wing; an auxiliary fuel tank; a detachable forwardly swept stub wing for supporting said tank and stabilizing said aircraft when said tank is filled, said stub wing and tank displacing the mean aerodynamic chord so that the center of gravity of said fuselage, swept back wing, stub wing and tank moves within an allowable percentage range of movement along the displaced chord; means for detaching said stub wing after said fuel tank is emptied, the stub wing and tank causing the center of gravity to move along the displaced chord beyond the allowable percentage range of movement, the center of gravity after the detachment of the stub wing and tank being restored to movement along said first mentioned chord and within the allowable percentage range.

ALEXANDER E. OSTROFF.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS France Feb. 23, 1942 v 

